Etching liquid and etching method

ABSTRACT

An object of the present invention is to provide: an etching liquid which is capable of etching titanium selectively in the presence of copper, and is further low in toxicity and excellent in storage stability; and an etching method using this etching liquid. The etching liquid of the present invention which is a liquid includes at least one acid selected from the group consisting of sulfuric acid, hydrochloric acid, and trichloroacetic acid, and at least one organic sulfur compound selected from the group consisting of a thioketone compound and a thioether compound, and makes it possible to etch titanium selectively in the presence of copper.

TECHNICAL FIELD

The present invention relates to an etching liquid for etching titaniumselectively in the presence of copper, and an etching method using thisetching liquid.

BACKGROUND ART

Hitherto, for the etching of titanium, an etching liquid containinghydrofluoric acid or hydrogen peroxide has been used. For example,Patent Document 1 suggests an etching liquid for etching titanium in thepresence of copper or aluminum, the pH of this liquid being adjustedinto the range of 7 to 9 with an aqueous solution including 10 to 40% byweight of hydrogen peroxide, 0.05 to 5% by weight of phosphoric acid,0.001 to 0.1% by weight of a phosphonic acid-based compound, andammonia.

However, the etching liquid containing hydrofluoric acid has a problemof being high in toxicity. The etching liquid containing hydrogenperoxide has a problem of being poor in storage stability.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: Japanese Patent No. 4471094

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In the light of the above-mentioned actual situation, the presentinvention has been made, and an object thereof is to provide an etchingliquid which is capable of etching titanium selectively in the presenceof copper, and is further low in toxicity and excellent in storagestability; and an etching method using this etching liquid.

Means for Solving the Problems

The etching liquid of the present invention is used to etch titaniumselectively in the presence of copper, and comprises:

at least one acid selected from the group consisting of sulfuric acid,hydrochloric acid, and trichloroacetic acid; and

at least one organic sulfur compound selected from the group consistingof a thioketone compound and a thioether compound.

It is preferred that the thioketone compound be at least one selectedfrom the group consisting of thiourea, diethylthiourea, andtrimethylthiourea.

It is preferred that the thioether compound be at least one selectedfrom the group consisting of methionine, ethionine, and3-(methylthio)propionic acid.

The etching liquid of the present invention preferably further comprisesan α-hydroxycarboxylic acid, and/or a salt thereof.

It is preferred that the α-hydroxycarboxylic acid be at least oneselected from the group consisting of tartaric acid, malic acid, citricacid, lactic acid, and glyceric acid.

It is preferred that the concentration of the acid(s) be from 20 to 70%by weight, and the concentration of the organic sulfur compound(s) befrom 0.01 to 10% by weight. The concentration of the α-hydroxycarboxylicacid and/or the salt thereof is preferably from 0.2 to 5% by weight.

The present invention also relates to an etching method, comprisingetching titanium selectively in the presence of copper by using theabove-mentioned etching liquid.

Effect of the Invention

The etching liquid of the present invention makes it possible to etchtitanium selectively in the presence of copper. Moreover, the etchingliquid of the present invention substantially contains neitherhydrofluoric acid nor hydrogen peroxide to be low in toxicity andexcellent in storage stability.

MODE FOR CARRYING OUT THE INVENTION

The etching liquid of the present invention is an aqueous solutionincluding at least one acid selected from the group consisting ofsulfuric acid, hydrochloric acid, and trichloroacetic acid, and at leastone organic sulfur compound selected from the group consisting of athioketone compound and a thioether compound.

Out of these acids, sulfuric acid is preferred from the viewpoint of alow volatility of the acid, and the stability of the etching speed ofthe etching liquid.

The concentration of the acid(s) in the etching liquid is notparticularly limited, and is preferably from 20 to 70% by weight, morepreferably from 30 to 60% by weight. If the acid concentration is lessthan 20% by weight, the etching liquid tends not to gain a sufficientspeed of etching titanium. If the acid concentration is more than 70% byweight, the safety of the etching liquid tends to become a problem.

The organic sulfur compound(s) has/have advantageous effects offunctioning as a reductant and a chelating agent.

Examples of the thioketone compound include thiourea, N-alkylthioureas,N,N-dialkylthioureas, N,N′-dialkylthioureas, N,N,N′-trialkylthioureas,N,N,N′,N′-tetraalkylthioureas, N-phenylthiourea, N,N-diphenylthiourea,N,N′-diphenylthiourea, and ethylenethiourea. The alkyl group(s) of anyone of the alkylthioureas is/are not particularly limited. The alkylgroup(s) is/are (each) preferably an alkyl group having 1 to 4 carbonatoms. It is preferred to use, out of these examples, at least oneselected from the group consisting of thiourea, diethylthiourea, andtrimethylthiourea, which are each excellent in advantageous effects offunctioning as a reductant or chelating agent, and in water solubility.

Examples of the thioether compound include methionine, a hydrochlorideof an alkyl ester of methionine, ethionine, 2-hydroxy-4-(alkylthio)butyric acids, and 3-(alkylthio)propionic acids. The number of carbonatoms in each of the alkyl groups is not particularly limited, and ispreferably from 1 to 4. These compounds may each be partiallysubstituted with one or more hydrogen atoms, or one or more hydroxylgroups, amino groups or other groups. It is preferred to use, out ofthese examples, at least one selected from the group consisting ofmethionine, ethionine, and 3-(methylthio)propionic acid, which are eachexcellent in advantageous effects of functioning as a reductant orchelating agent.

The concentration of the organic sulfur compound(s) in the etchingliquid is not particularly limited, and is preferably from 0.01 to 10%by weight, more preferably from 0.2 to 5% by weight. If theconcentration of the organic sulfur compound(s) is less than 0.01% byweight, the etching liquid can gain neither a sufficient reducingperformance nor a sufficient chelating effect so that the speed ofetching titanium tends to be insufficient. If the concentration is morethan 10% by weight, the dissolution of the organic sulfur compound(s) inthe etching liquid tends to reach a limit.

The etching liquid may include an α-hydroxycarboxylic acid, and/or asalt thereof. The α-hydroxycarboxylic acid, and the salt thereof haveadvantageous effects of functioning as a chelating agent for titanium,and can therefore restrain the generation of any precipitation oftitanium in the etching liquid. Examples of the α-hydroxycarboxylic acidinclude tartaric acid, malic acid, citric acid, lactic acid, andglyceric acid.

The concentration of the α-hydroxycarboxylic acid and/or the saltthereof in the etching liquid is not particularly limited, and ispreferably from 0.2 to 5% by weight, more preferably from 0.5 to 2% byweight from the viewpoint of the chelating effect and the solubilitythereof.

The etching liquid may include sulfurous acid and/or a sulfite thereof.Sulfurous acid and the sulfite thereof have advantageous effects offunctioning as a reductant, and can therefore improve the speed ofetching titanium.

The concentration of sulfurous acid and/or the sulfite thereof in theetching liquid is not particularly limited, and is preferably from 0.02to 0.5% by weight, more preferably from 0.05 to 0.2% by weight from theviewpoint of the reducing performance and odor thereof.

Besides the above-mentioned components, any other component may be addedto the etching liquid as far as the advantageous effects of the presentinvention are not hindered. Examples of the other component include asurfactant, a component stabilizer, and an antifoaming agent.

The etching liquid can easily be prepared by dissolving theabove-mentioned individual components into water. The water ispreferably water from which ionic substances and impurities have beenremoved. The species of the water is preferably, for example, ionexchange water, pure water, and super pure water.

About the etching liquid, it is allowable to blend the individualcomponents with each other to have predetermined concentrations,respectively, when the etching liquid is used; or prepare a concentratedliquid of the etching liquid beforehand, dilute the concentrated liquidimmediately before the use, and then use the diluted liquid.

An etching method using the etching liquid of the present invention isnot particularly limited. Examples of the method include a method ofcoating or spraying the etching liquid onto a target object containingcopper and titanium, and a method of immersing a target objectcontaining copper and titanium into the etching liquid. The treatmenttemperature is not particularly limited, and is preferably from 40 to70° C., more preferably 45 to 55° C. from the viewpoint of the etchingspeed of the etching liquid, and safety. The treatment period is variedin accordance with, for example, the surface state and shape of thetarget object. The period is usually from 30 to 120 seconds.

EXAMPLES

The following will describe working examples of the present inventiontogether with comparative examples. The invention should not beinterpreted to be limited to the working examples described below.

Each etching liquid was prepared to have one out of compositions shownin Tables 1 and 2. Under conditions described below, an etching test andan etching liquid stability test were conducted. In the etching liquidof each of the compositions shown in Tables 1 and 2, the balance thereofwas made of ion exchange water. Each concentration of hydrochloric acidshown in Tables 1 and 2 is the concentration of the acid as hydrogenchloride.

(Etching Test)

A titanium film was formed into a thickness of 50 nm onto each resinpiece by sputtering, and next a copper film was formed into a thicknessof 200 nm onto the titanium film. Furthermore, a pattern was formedthereon by electroless plating. The resultant substrate was used as eachsample. An etching liquid for copper was used to dissolve the sputteredcopper film of the sample to make the titanium film naked. Thereafter,any one of the samples was immersed in the etching liquid of each ofExamples 1 to 12 and Comparative Examples 1 to 3 to make an etchingtest. The results are shown in Table 1.

TABLE 1 Treating Percent temper- Etching speed by ature (nm/min.) weight(° C.) Titanium Copper Example 1  Sulfuric acid 55 50 30 <10Diethylthiourea 5 Example 2  Hydrochloric 30 50 35 <10 acidDiethylthiourea 5 Example 3  Sulfuric acid 55 50 50 <10Trimethylthiourea 3 L-lactic acid 1 Example 4   Sulfuric acid 55 50 60<10 DL-methionine 2 L-lactic acid 1 Example 5  Sulfuric acid 55 50 85<10 3-(Methylthio) 2 propionic acid L-lactic acid 1 Example 6  Sulfuricacid 55 50 35 <10 Diethylthiourea 5 L-lactic acid 1 Sulfurous acid 0.2Example 7  Sulfuric acid 55 50 55 <10 Trimethylthiourea 3 L-lactic acid1 Sulfurous acid 0.2 Example 8  Sulfuric acid 55 50 30 <10Diethylthiourea 5 Citric acid 2 Example 9  Sulfuric acid 55 50 30 <10Diethylthiourea 5 Tartaric acid 1 Example 10 Sulfuric acid 55 50 75 <10Ethionine 1 Tartaric acid 1 Example 11 Sulfuric acid 50 50 90 <10Trichloroacetic 5 acid DL-methionine 2 Citric acid 2 Example 12Hydrochloric acid 30 50 40 <10 Trimethylthiourea 3 Tartaric acid 1Comparative Sulfuric acid 55 50 <10 <10 Example 1   L-lactic acid 1Comparative Diethylthiourea 5 50 <10 <10 Example 2   L-lactic acid 1Comparative Acetic acid 60 50 <10 <10 Example 3  Diethylthiourea 5L-lactic acid 1

As shown in Table 1, the etching liquid of the present invention makesit possible to etch titanium selectively without etching copper.

(Stability Test of Etching Liquids)

The respective etching liquids of Examples 1, 7 and 12, and ComparativeExample 4 were allowed to stand still at room temperature for 2 days,and then the same test as described above was conducted. The etchingspeed of each of these examples before the still standing was comparedwith that after the still standing. The results are shown in Table 2.

TABLE 2 Before still After still standing standing for 2 days PercentTreating Etching speed Etching speed by temperature (nm/min.) (nm/min.)weight (° C.) Titanium Copper Titanium Copper Example 1 Sulfuric acid 5550 30 <10 30 <10 Diethylthiorea 5 Example 7 Sulfuric acid 55 50 55 <1055 <10 Trimethylthiourea 3 L-lactic acid 1 Sulfurous acid 0.2 Example 12Hydrochloric acid 30 50 40 <10 40 <10 Trimethylthiourea 3 Tartaric acid1 Comparative Hydrogen peroxide 10 35 100 <10 25 <10 Example 4 Ammonia0.3

As shown in Table 2, the etching liquids of the present invention areexcellent in storage stability, and makes it possible to etch titaniumselectively even after stored over a long term.

1. An etching liquid for etching titanium selectively in the presence ofcopper, comprising: at least one acid selected from the group consistingof sulfuric acid, hydrochloric acid, and trichloroacetic acid; and atleast one organic sulfur compound selected from the group consisting ofa thioketone compound and a thioether compound.
 2. The etching liquidaccording to claim 1, wherein the thioketone compound is at least oneselected from the group consisting of thiourea, diethylthiourea, andtrimethylthiourea.
 3. The etching liquid according to claim 1, whereinthe thioether compound is at least one selected from the groupconsisting of methionine, ethionine, and 3-(methylthio) propionic acid.4. The etching liquid according to claim 1, further comprising anα-hydroxycarboxylic acid, and/or a salt thereof.
 5. The etching liquidaccording to claim 4, wherein the α-hydroxycarboxylic acid is at leastone selected from the group consisting of tartaric acid, malic acid,citric acid, lactic acid, and glyceric acid.
 6. The etching liquidaccording to claim 1, wherein the concentration of the acid(s) is from20 to 70% by weight, and the concentration of the organic sulfurcompound(s) is from 0.01 to 10% by weight.
 7. The etching liquidaccording to claim 4, wherein the concentration of theα-hydroxycarboxylic acid and/or the salt thereof is from 0.2 to 5% byweight.
 8. An etching method, comprising etching titanium selectively inthe presence of copper by using the etching liquid recited in claim 1.